AMSTERDAM, Netherlands-Large subgroups of patients with non-metastatic breast cancer treated with breast-conserving therapy (BCT) plus radiation therapy had longer median overall and breast cancer specific survivals (OS and BCSS) than retrospectively matched patients with similar disease who had mastectomies-with or without radiotherapy. These results were found from among 129,692 patients in the Netherlands Cancer Registry in two different time cohorts (Eur J Cancer 2017;72(1):S2-S3).
Breast Cancer Specific Survival
"We saw that-in some groups-patients could benefit more from breast-conserving therapy-[and] so had a better breast cancer specific survival than patients [with] mastectomy," said Sabine Siesling PhD, Professor of Clinical Epidemiology at the Netherlands Comprehensive Cancer Center in the University of Twente. "We saw the most benefit in patients who did not receive chemotherapy, with comorbidity, or who were older than 50 years of age."
BCSS for women over 50 was more than 25 percent longer in women with non-metastatic tumors up to 5 cms, with or without lymph node invasion (T1-2N0-1) who had BCT as compared with similar patients treated with mastectomy.
Overall Survival
OS was improved by almost the same amount. "Comparing breast-conserving therapy to mastectomy we saw hazard ratios of 0.70, which means about 25-30 percent higher risk of dying in the mastectomy group.
"Of course, it's a retrospective study so we are not looking at a causal relationship but an association," said Siesling, noting that in OS confounding factors could have had more influence. "So that was the reason why we looked specifically [at] breast cancer specific survival."
BCT Benefit
The study concluded that a possible benefit had been identified from BCT in some of the predefined patient sub-groups.
The overall finding of an association with BCT and longer survival also was seen in each of the time cohorts of the study individually.
"We looked at two different groups [diagnosed between 1999 and 2005 and between 2006 and 2012] in order to allow us to compare long-term outcomes in a more historical versus a more recent cohort, evaluating patients that had been able to benefit from more sophisticated diagnostics and therapies," said Siesling.
BCSS was significantly longer in patients treated with BCT compared with those having mastectomy in the earlier cohort (with a hazard ratio (HR) of 0.72), and OS was significantly extended (with an HR of 0.74). Similarly in the later cohort, BCT also was associated with significantly longer BCSS (HR 0.75) and OS (HR 0.67).
Siesling acknowledged she could not give a biological explanation for the findings. "We do not have enough information [to explain] the results we see, but I think these are the best data to use because we will never do a trial comparing both surgical therapies in the future."
Individualize Surgery
In terms of clinical decision-making, Siesling said doctors should take these results into account. "For instance, when you have elderly patients with co-morbidities, you should really consider breast-conserving therapy as a safe option," she said.
Although the study findings support a change of practice towards BCT, she said this depended on shared decision-making. And she added that other factors needed to be considered that could make mastectomy a good choice.
"We would like to emphasize that these results do not mean that mastectomy is a bad choice. For patients for whom radiotherapy is not suitable or feasible due to social circumstances, for whom the risk of late side effects of radiotherapy is high, or who have the prospect of a poor aesthetic outcome following BCT, a mastectomy may still be the preferable treatment option," Siesling said.
"The bottom line is that breast-conserving therapy is a safe option compared to mastectomy. Our study showed that BCT is at least as good as mastectomy and that some patients might benefit more than others from BCT in the future."
Michael Baumann MD, Chair of Radiation Oncology at the University of Dresden, Germany, Scientific Chair of the German Cancer Research Center, Heidelberg, and Scientific Chair of ECCO 2017, said it was very difficult to understand the mechanism causing the associations Siesling had reported.
"But-as we know-mastectomy is a more debilitating procedure than breast-conserving surgery and, therefore, it might be that we have [overlooked] something in the past which really explains this," Baumann concluded. "At the moment, breast-conserving therapy is very well-founded on indications which are in guidelines, and doctors should continue to use that guidelines."
Peter M. Goodwin is a contributing writer.